Electrochromism is a phenomenon in which a color is reversibly changed by the direction of an electric field when a voltage is applied. An electrochromic material is a material, an optical property of which can be reversibly changed by an electrochemical redox reaction having the electrochromism property. The electrochromic material is not colored when an electrical signal is not applied from the outside, but it is colored when the electrical signal is applied. On the contrary to this, when the electrical signal is not applied from the outside, the electrochromic material is colored, but when the electrical signal is applied, the electrochromic material is not colored.
An electrochromic device, which is a device using a phenomenon in which the light transmission of an electrochromic material is changed by an electrochemical redox reaction, has been used for adjusting the light transmission or reflectance of a window glass for building or a mirror for automobiles. Recently, as the electrochromic device has been known to have an infrared cutoff effect as well as a color variation in a visible ray area, it has been receiving a great deal of attention with regard to the possibility of application as an energy-saving type product.
In particular, when the electrochromic device is applied to a rear view mirror, a vehicle window, a sun roof, and the like, it functions to stably protect a driver's field of vision by providing a variation in reflectance depending upon discoloration of the mirror at the same time as automatically sensing the strong beam of a car reflected from a car mirror in the daytime or at night.
FIG. 1 is a view schematically illustrating the structure of a conventional electrochromic display device.
Referring to FIG. 1, the conventional electrochromic display device is configured such that a first transparent substrate 10 and a second transparent substrate 20 facing each other are disposed to be spaced apart from each other; an electrode 30 and a reflection layer 40 are formed on respect facing surfaces of the first and second transparent 10, 20; a space is formed between the electrode 30 and the reflection layer 40 using a sealant 50; an electrochromic material layer 60 is formed by injecting a liquid discoloration material and an electrolyte into the formed space; and electrode connection parts 70, 80 are formed at one end of the first transparent substrate 10 and the transparent electrode 30, and at one end of the second transparent substrate and the reflection layer 40. The conventional electrochromic display device functions to protect a driver's field of vision by applying an electrochromic material in a liquid state to reduce the reflectance of light.
FIG. 2 illustrates a formation process of the electrochromic material layer of the conventional electrochromic display device.
Referring to FIG. 2, the first transparent substrate is prepared as shown in (A) of FIG. 2. More specifically, the first transparent substrate on which the transparent electrode is formed is prepared. Also, the second transparent substrate on which the reflection layer is formed may be prepared.
Then, as shown in (B) of FIG. 2, an upper portion of the transparent electrode is subjected to side sealing using the sealant 50. At this time, an injection hole 54 into which an electrochromic material and an electrolyte are injected is formed. Accordingly, the side sealing causes a spaced portion by the injection hole 54 rather than causing a continuous ring-like shape on the transparent electrode. As previously described regarding (A) of FIG. 2, when the second transparent substrate on which the reflection layer is formed is prepared, the reflection layer may be subjected to side sealing.
Then, as shown in (C) of FIG. 2, after bonding the second transparent substrate (20) on which the reflection layer is formed, and the first transparent substrate on which the transparent electrode 30 is formed, an electrochromic material and an electrolyte are injected via the injection hole 54 in a vacuum state.
After this, as shown in (D) of FIG. 2, the electrochromic material layer is formed by sealing the injection hole 54 using an end sealing 55.
As such, with regard to the conventional electrochromic device, when the electrochromic material layer is formed, external air and moisture should be blocked in order to increase the durability of an electrochromic function. To do so, by boding the first and second transparent substrates, the electrochromic material and the electrolyte should be injected in a vacuum state.
However, as the electrochromic display device has become bigger, such a vacuum injection method is problematic in that a time required for injection is largely increased so that production efficiency is reduced, and production costs is increased.
Also, in order to maintain an electrochromic state of the electrochromic material in the liquid state, a voltage should be continuously applied. Thus, it is problematic in that high power consumption is required, and a reaction speed is slow upon decolorization. Furthermore, the electrochromic material in the liquid state is problematic in that uniform discoloration is not performed upon discoloration.